Case 1: Intro to immunology (innate & adaptive) Flashcards
Function of immune system
protect the body from foreign challenges by:
- immune recognition
- immune effector functions
- immune regulation
- immune memory
Define Antigen
molecules which are able to induce immune responses, can be lipids, proteins, nucleic acids, or organic molecules.
What are epitopes?
Parts of antigens that interacts with antigen receptors
Types of immune tissues
- Non-specific barriers (e.g. skin)
- MALT
- Primary immune tissue (bone marrow & thymus)
- Secondary immune tissue (lymph nodes & spleen)
Outline the non-specific immunity of skin
- mechanical protection: provided by tight junctions of epithelial cells. Longitudinal of air or fluid removes attached pathogens
- chemical protection: provided by the secretion of anti-microbial peptides and fatty acids
- microbiological protection: provided by normal flora that depletes nutrients and provides hostile environment for pathogen proliferation
Outline the innate immunity located in the skin and its collaboration with adaptive immunity
- specialist APC (Langerhans cells) in the skin samples antigen
- Langerhans cells leave the skin and enter the lymphatic system
- mature dendritic cells enter lymph nodes and transfer some antigens on resident dendritic cells
- activation of B cells/T cells
Outline the antigen sampling process in the gut
- bacterium sampled by M cell
- M cell passes on antigen to professional APC (dendritic cell)
- dendritic cell migrates to local MALT, activating B/T cells
- antibody production (mostly IgA in the gut)
List the primary and secondary immune tissues
- Primary:
1. Bone marrow
2. Thymus - Secondary:
1. Lymph nodes
2. Spleen
3. MALT
Function of the bone marrow
- production of all immune cells in the adult by haematopoiesis.
- haematopoiesis: a process whereby stem cells are differentiated into myeloid or lymphoid progenitor cells, and thereafter further specialised into various components of the immune system
The character and functions of myeloid cells
*Myeloid cells leave the bone marrow fully mature and functional
- Phagocytes:
a) Neutrophil - phagocytosis & activation of bactericidal mechanisms
b) Macrophage - same as above & APC
c) Dendritic cells - antigen uptake in periphery sites & APC
- Inflammatory mediators:
a) Basophil - exact function unknown
b) Eosinophil - killing of antibody coated parasites
c) Mast cells - degranulation (release of histamine and active agents)
The character and functions of lymphoid cells
- Leave the bone marrow and undergo further specialisation in lymphoid tissue. B and T cells acquire antigen receptors in the primary lymphoid organs, becoming Naive B/T cells which migrate to secondary lymphoid organs where they encounter antigens. Upon activation, B and T cells become effector cells that can circulate the body (only 2% of lymphocytes are in the bloodstream).
1. NK cells - release lytic granules that kill some virus-infected cells
2. B cells - develop in bone marrow, differentiate and mature in spleen and lymph nodes. Recognise antigens via BCR and when activated undergo monoclonal expansion. Terminally differentiate into plasma cells
3. T cells - develop in bone marrow and mature in thymus. Antigen recognition via TCR & can only recognise processed peptide antigens that are presented on MHC on APC. This is because the epitopes that are recognised by T cells are often buried deep in an antigen, therefore APCs have to process them into peptide fragments in order to expose epitope. The fragment then binds to MHC on the APC forming an MHC-peptide complex to which TCR binds.
Function and features of the lymph node
- filters antigen from tissue, return blood via the thoracic duct.
- primary follicles mostly contain naive B cells
- secondary follicles contain germinal centre where B cells have undergone monoclonal expansion
- T cells are located in parafollicular region
